Electronics > Beginners

TL071 distortion - bad amplifier design?

<< < (16/26) > >>

AngraMelo:
I see! So you are talking about this circuit (attached)
Ill make all the changes.
What should be the voltage ratings of the 100uf caps?

spec:
UPDATE #1  2018_12_12 (please see reply #79)


--- Quote from: AngraMelo on December 12, 2018, 01:23:00 am ---Spec, I did only the following modifications:
- Changed the 2 4.7nF for 2 47uF capacitors
- Added a BC337 between the collectors of both VAS transistors
- added a 1k resistor between 1015 collector and BC337 base
- added a 1k pot between 1815 collector and BC337 base
- added a 100uf cap across the BC337 collector and emitter
I believe that is all that is included in the schematic I posted on reply#71, am I mistaken?
--- End quote ---
No, not mistaken. That is correct but, I now think that you need to do all reply #44 mods- I am not able to determine the VAS current of the original design. Perhaps you could measure the VAS current of the original design.


--- Quote from: AngraMelo on December 12, 2018, 01:23:00 am ---Do I need to short the input to measure the current?
--- End quote ---
No, but it would be a good idea. :)

Zero999:

--- Quote from: AngraMelo on December 12, 2018, 01:29:59 am ---I see! So you are talking about this circuit (attached)
Ill make all the changes.
What should be the voltage ratings of the 100uf caps?

--- End quote ---
The ones on the 15V zener diodes should be rated to at least 20V, to allow for the fact that the zener diode voltage might be higher than 15V.

The one on the BC556 can be a much lower voltage rating, say 6.3V, because the voltage across the BC556 is a couple of volts at most.

Of course higher voltage rating capacitors can be used, so 25V, 35V etc. is fine for all 100μF capacitors in the circuit.

spec:

--- Quote from: AngraMelo on December 12, 2018, 01:29:59 am ---I see! So you are talking about this circuit (attached)
Ill make all the changes.
What should be the voltage ratings of the 100uf caps?

--- End quote ---
Yes, that is the correct circuit. The second added transistor can be most small signal PBJTs.
The 100uF cap only needs to be 4V7 or more. The 100uF capacitor only has 1V2 across it in normal operation of the amp.

Apologies for causing you extra work.

spec:

--- Quote from: AngraMelo on December 12, 2018, 01:29:59 am ---I see! So you are talking about this circuit (attached)
Ill make all the changes.

--- End quote ---
This is an update on the subject of the original schematic VAS current (now that I have slept on it).

When I proposed the BC337 VBE multiplier for use with the original VAS, I had assumed a VAS current of 5mA to 10mA, because that sort of current is normal for a VAS and I thought I had also calculated the VAS current to be around 10mA. But that is obviously not the case because, after just doing an analysis, I find that the VAS current is in fact indeterminate, but a low value in any case. This would explain why the VBE multiplier did not work with the original VAS.

So just to confirm, I would advise to get your amplifier to the reply #44 schematic build state and I will now leave that schematic as is and not update it further so that it acts as a reference point.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod